The present invention relates generally to improvements in needle valves, and more particularly, but not by way of limitation, to the construction of seats that receive the needle of the valve.
A known type of valves is one in which a frusto-conical valve member, or needle, is mounted on a valve body for axial movement along a valve closure axis into, and out of, a frusto-conical valve seat cavity. Flow passages, opening into the valve seat cavity, are formed in the valve body so that the valve can be closed by inserting the needle into the valve seat cavity and opened by withdrawing the needle from the valve seat cavity.
In many cases, the valve seat cavity is formed in a valve seat that is situated in a chamber formed in the valve body and openings are formed through the wall of the valve seat to extend the flow passages into the valve seat cavity. The valve seat, in such case, is provided with a locking system of some type so that the openings through the walls of the valve seat are maintained in alignment with the portions of the flow passage that extend through the valve body.
A problem that has occurred with valves of this type is that the valve member tends to expand the valve seat when the valve is closed, because of the frusto-conical shapes of the valve member and the valve seat cavity, and the openings formed through the seat to extend the flow passages of the valve into the valve seat cavity weaken portions of the valve seat at the location at which sealing of valve seat cavity is effected to close the valve. Should the valve member be forcefully inserted into the valve seat cavity, as will often happen when the user closes the valve, the valve seat has a tendency to break at the openings formed at the wall thereof with result that the valve will leak.